1. Field of the Invention
The present invention is generally directed to the field of oilfield production equipment, and, more particularly, to an injector head for inserting and withdrawing coiled tubing into and from a well.
2. Description of the Related Art
After wells are drilled into the earth, coiled tubing is often inserted into and withdrawn from a well for a variety of purposes. For example, coiled tubing may be inserted to produce hydrocarbons, i.e., oil and gas, to inject various fluids to stimulate the production of hydrocarbons, to clean various portions of the well, etc. As is well known by those skilled in the art, coiled tubing is a relatively small, continuous length of thin-walled tubing that has an outside diameter varying from approximately xc2xdxe2x80x3-3xc2xdxe2x80x3. It is envisioned that even larger sizes of coiled tubing may be used in the future.
Tubing is typically supplied on a large spool that contains many thousands of feet in a coiled arrangement. In practice, the spool of tubing is mounted on a large truck that is positioned adjacent the well. The coiled tubing may be continuously fed into or withdrawn from a well using what is generally known in the industry as a coiled tubing injector head. Injector heads vary in design and construction from manufacturer to manufacturer. However, most injector heads are comprised of a pair of opposed endless chain loops that carry a plurality of gripper blocks that are pressed against and grab generally opposed sides of the coiled tubing when it is inserted therebetween. Typically, the endless chains are mounted on an arrangement of drive sprockets and idler sprockets or rollers, and the chains are driven by one or more hydraulic or electric motors. In this manner, the gripper blocks positioned on the endless chains act to grab and push (insertion operation) or pull (withdrawal operation) the coiled tubing as the endless chain moves. Illustrative examples of some of the various types of injector heads known in the industry are set forth in U.S. Pat. Nos. 4,585,061, 4,655,291, 5,133,405, 5,188,174, 5,309,990, 5,553,668, and 5,566,764, all of which are hereby incorporated by reference in their entirety. However, there are many problems associated with currently known injector heads.
The endless chains used in modem injector heads are sometimes comprised of a plurality of one-piece gripper blocks that are positioned between two rollers of a triple-wide chain through the use of one or more pins. See, e.g., FIG. 9 of U.S. Pat. No. 4,585,061 and FIGS. 5 and 6 of U.S. Pat. No. 5,188,174. During the course of manufacturing the injector head, this design necessitates that the manufacturer of an injector head take a standard triple-wide chain, or at least components of it, and assemble what is a special chain assembly. As can be appreciated by those skilled in the art, this can be a very time-consuming and expensive process. For example, a manufacturer might purchase a traditional triple-wide roller chain, remove the middle roller section, and install a plurality of one-piece gripper blocks on multiple master links that are used to secure the chain together. These master links are positioned within openings formed in the gripper block. See, e.g., FIG. 9 of U.S. Pat. No. 4,585,061. Alternatively, the gripper blocks may be secured to the chain by multiple pins that do not extend completely through the gripper blocks. See, e.g., FIGS. 5 and 6 of U.S. Pat. No. 5,188,174. In such configurations, the gripper blocks, typically comprised of an investment cast steel, engage the master links and/or pins. This type of engagement is subject to excessive wearing. Moreover, the chains, when disassembled and/or reassembled in this manner, no longer comply with various standard setting bodies, such as ISO9000 or API.
With either technique, as well as others not specifically described above, prior art devices often required the injector head manufacturer to spend many hours assembling and disassembling the endless chains used in the injector heads. These type of designs also caused problems beyond those encountered during the initial assembly of the injector head. For example, replacement of a gripper block on one of the aforementioned injector heads requires manipulation and at least partial removal of some of the pins securing the gripper block to the chain. In some cases, removal of one or more gripper blocks required disassembly of the chain entirely. Moreover, if it was deemed necessary to replace the gripper blocks to accommodate different diameter coiled tubing, the process involved could be very time-consuming and require complete disassembly and reassembly of the chain.
Additionally, other types of injector heads employ gripper blocks with removable inserts that are coupled to the gripper block body by a plurality of fasteners, e.g, socket head bolts or socket head screws. In these type of systems the fasteners became loose during operation, causing maintenance problems and downtime. These type of systems typically required repeated tightening of the fasteners, which caused delay and subjected the fasteners to higher stresses.
Another problem encountered with existing injector head designs relates to bearing skates employed in such devices. Injector heads typically involve the use of one or more bearing skates that are used to transmit a gripper force to the gripper blocks positioned in the endless chain. The bearing skates are typically coupled to one or more hydraulic cylinders that, when actuated, tend to force the gripper blocks together, thereby asserting a gripping force on the coiled tubing positioned between the gripper blocks. See, e.g., the skate and hydraulic cylinder arrangement described at, for example, column 6, line 37, to column 7, line 38, of U.S. Pat. No. 5,188,174. The bearing skates used in modem injector heads also contain a number of bearings that are adapted to rollingly engage a portion of the gripper blocks to transmit the force supplied by the hydraulic cylinders to the gripper blocks. With prior art injector heads, the bearings used on bearing skates were arranged in an in-line, non-staggered arrangement. See, e.g., FIG. 4 of U.S. Pat. No. 5,188,174. Such an in-line bearing arrangements lead to numerous problems. For example, using prior art in-line bearing arrangements, fewer bearings were in contact with a given gripper assembly, i.e., the number of bearings that were able to contact and support any particular gripper block was limited. With fewer bearings available to contact the gripper block, bearing loading increased and, as might be expected, bearing life decreased. These factors tend to lead to reduced operating time, reduced life and increased maintenance for a given injector head employing a bearing skate having a traditional in-line bearing arrangement.
Another problem encountered with existing injector heads is the overall weight of such devices. As stated previously, coiled tubing comes in many sizes. Currently, coiled tubing is used in sizes ranging from approximately xc2xdxe2x80x3 to 3xc2xdxe2x80x3 in diameter. It is anticipated that even larger coiled tubing will be used in the future. However, current injector heads are designed on a worst case basis. That is, currently available injector heads are designed such that all components, e.g., frame, gears, motors, etc., are capable of withstanding all anticipated forces that will be encountered during the injection and withdrawal of at least the largest diameter coiled tubing. In turn, this process leads to an injector head that is excessively heavy. While this design strategy adds cost to the initial manufacture of the injector head, which is undesirable in and of itself, the increase in the weight of the injector head is very undesirable.
As those skilled in the art understand and appreciate, an injector head is typically transported to the site of the well by truck. Typically, the weight of these injector heads may vary between approximately 7,000-14,000 pounds. The Federal Department of Transportation (DOT) has very strict limitations on the shipping weight of articles, including injector heads, that are transported on our nation""s highways and bridges. Thus, it is desirable to have an injector head that, while still capable of being used with a full range of existing sizes of coiled tubing, weighs less than prior art injector heads.
With existing coiled tubing injector heads, in normal operation, the distances between various components remains relatively fixed regardless of the size of tubing used. For example, current injector heads are designed to accommodate at least the largest anticipated coiled tubing size, i.e., the injector heads are designed for a worst case design. As stated previously, coiled tubing may vary in diameter from approximately xc2xdxe2x80x3 to 3xc2xdxe2x80x3, and even larger sizes are anticipated to be used in the future. However, most of the coiled tubing applications involve coiled tubing having a diameter less than 3xe2x80x3. For example, it is believed that less than five percent of the coiled tubing applications involve coiled tubing having a diameter of 3xe2x80x3 or greater.
On existing injector heads that are designed to accommodate both the smaller and larger sizes of coiled tubing, the distance between the centerline of the tubing and the centerlines of the respective endless chains remains fixed at a distance that will accommodate the larger diameter coiled tubing. To use these type of injector heads with smaller diameter coiled tubing, the size of the gripper block must be effectively increased. This may be accomplished by installing larger gripper blocks and/or by installing inserts on existing gripper blocks. These modifications are made so as to allow the gripper blocks to reach the smaller diameter tubing. These larger gripper blocks and/or inserts increase the weight of an already heavy injector head. Moreover, the effort to change out these gripper blocks and/or inserts can be quite time-consuming and expensive.
The present invention is directed to an apparatus for solving, or at least reducing the effects of, some or all of the aforementioned problems.
The present invention is directed to an injector head having a plurality of endless chains, the endless chains having a plurality of links. The invention further comprises a plurality of gripper block assemblies positioned around the links of the endless chains.
In another aspect of the present invention, an injector head is comprised of a plurality of ISO9000 or API certified endless chains, said chains having a plurality of links and a plurality of multiple-piece gripper block assemblies.